I am a ballet dancer who has been diagnosed with Os trigonum syndrome can I keep dancing?

The best option for you is to remove the aggravating factor from your daily routine.  Symptoms can often diminish with rest, thus it is best to stop performing the specific triggering activity.  If you continue to dance on pointe or demi-pointe not only is an increase in pain possible, this can lead to compensations in form which can predispose you to additional injuries.